The present invention belongs to the technical field of mechanical drive, which relates to a mechanical continuously variable transmission, specifically to a mechanical continuously variable transmission that can output a large torque and larger speed ratio, as well as provides a constant-ratio transmission that can output a large torque.
In the present technology, most mechanical devices which need to change speed, such as vehicle, vessels, engineering machine, factories and mines and harbors machine etc, continuously speed is superior to step speed change, firstly because it simplifies the manipulation, and secondly the speed variation is smooth, which is quite favorable to the vehicles, and especially it can realize the best match between transmission systems and engine operating modes, which is favorable to the working life of the engines and energy conservation.
Due to above advantages of the Continuously Variable Transmission (CVT), there are kinds of CVT developed, wherein the friction transmission of conical-plate is widely used. However, this transmission have intrinsic defects that is difficult to overcome, such as its output torque being small, most below 300 Nm, which can hardly apply to motor vehicles of great displacement, furthermore, it can more hardly be satisfied for larger requirement of output torque, such as trucks, diesel locomotives, tanks and watercrafts. Moreover, its speed regulation range, i.e., speed ratio is restricted, normally not more than 6:1. Therefore it needs to suit with transmission of fixed speed ratio. A more realistic problem is that this transmission requires higher quality and technical requirement for the drive chains or drive belts, resulting in the cost of making and using transmissions increase highly, which is disadvantageous for the popularity and generalization of this transmission.
The publicized patent application titled “a large-torque breaker-roller type constant ratio/continuously variable transmission” (hereafter referred to “breaker-roller type”), with application number of 200910136244.1, publicized a large-torque breaker-roller type continuously variable transmission and this transmission introduced the concept of breaker roller, which was consisted of two pairs of breaker-rollers of driving roller and driven roller. Each pair of breaker roller was two drive rollers operating synchronously. A drive chain rotated n cycles outside the driving breaker rollers and directed to the driven breaker rollers to rotate n cycles on them and returned to the driving breaker rollers to form a closed circle. Due to effective augment of wrap angles between the chain belt and the drive rollers, the skidding in driving was avoid, achieving a large power (torque) output. However, this breaker-roller type transmission needs two pairs of breaker-rollers that is four rollers, resulting in the structure being larger.